Light-initiated polymerization at low intensity reduces contraction stresses of resin composites and the improvement of cavity adaptation is attempted. However, the light intensity has a large effect on the degree of conversion particularly at the bottom of a composite restoration. Then the light intensity of the light transmitted through 1, 2 or 3 mm thick resin composites (3 products, 4-6 shades) was measured. The output to the lamp of light source is 7, 8, 9, 10, 11 or 12 V. As the result, there was a significant difference in the transmitted light intensity among products and shades at either output. "Slow setting" method (250mW/cmィイD12ィエD1 × 20s, 10s pause, 600 mW/cmィイD12ィエD1 × 20s) which applied the light-initiated polymerization at low intensity was compared with the usual irradiation method (700 mW/cm2 × 40s). And there was a significant difference in the adaptation of cylindrical dentin cavity among used dentin adhesive systems and it tended to show cavity adaptation in which
… More"slow setting" method was good at the line angle and cavity floor. In addition, in order to examine elasticity of the hybrid layer and its surrounding area the elasticity of dentin surfaces, etched/primed dentin surfaces and bonding resin surfaces was calculated from the indentation depth measured by an indentation tester. The elasticity of 2 mm thick resin composites irradiated at low light intensity (8V) and usual light intensity (11V) was also calculated. Used materials were 3 dentin adhesive systems (One-step, Singlebond, Liner bond II Σ) and 3 resin composites (Aelitefil, Z100, AP-X).As the result, in Liner bond IIΣ, there was no significance between the etched/primed dentin surface and the bonding resin surface but there was the significance in One-step and Singlebond. Though in 8V, there was no significance except for Singlebond between the bonding resin surface and the resin composite basal surface, in 11V, there was the significance in all 3 types (One-step/Aelitefil,Singlebond/Z100, Liner bond II Σ/AP-X). Less